This invention relates to a screen-segmented display device in a display apparatus, or more in particular to a device for controlling the movement of a cursor for designating the writing position of data on the display screen.
In an apparatus for displaying characters or symbols on the CRT screen, the CRT screen is segmented into a multiplicity of small portions so that one character or symbol is displayed in each of the portions. A CRT screen with the scan of 16 lines and 40 columns, for example, will display 640 portions. In writing a character or symbol in a portion on the CRT screen, a short bright line called a cursor is displayed on the under side of the particular portion to designate the writing position. After moving the cursor to the desired position, a character code is supplied to the CRT display apparatus from the keyboard or an external computer, thus enabling accurate writing of data in the designated position on the screen.
The address of the cursor is generally determined by storing the related horizontal and vertical addresses in a cursor register. This address is subject to change in response to a command signal from the keyboard or an external computer. Following the writing of a character in the position on the screen designated by the cursor, the data in the cursor register is automatically updated to proceed to the next characterwriting position. When the cursor reaches the extreme right end of a line, it is automatically relocated to the left end of the next line. In this way, the cursor is moved to the bottom line in sequence.
In a well-known display apparatus, the required information, such as headings, are displayed on the screen according to a predetermined program so that data corresponding to each heading is adapted to be written at the side of the particular heading in response to the cursor designation by way of the keyboard. This type of CRT display apparatus is usually provided with a cursor skip function whereby the cursor is directly moved to the next writing position by skipping those headings to be fixedly displayed or sections to be left blank, thus eliminating an erroneous writing or erasure of headings.
As explained above, the cursor is moved from left to right ends of the screen line by line while skipping those portions requiring no writing. Assume that the screen is divided into two parts laterally, i.e., into right and left sections. The cursor starts at the left end of the first line in the left screen section and is moved from the first line in the left screen section to the first line in the right screen section, the second line in the left screen section, the second line in the right screen section, to the third line in the left screen section, and so on. Since the right and left screen sections are displayed in independent data blocks, the line-by-line alternate data writing in left and right screen sections complicates not only the writing operation but also the program processing. A suggested method for obviating this shortcoming consists in formulating a program so as to move the cursor line-by-line first only in the left screen section, followed by line-by-line movement in the right screen section. The disadvantage of this method is the complexity of programming resulting from the line-by-line movement of the cursor in each screen section.